I had to google the source of "Dopp", which I heard years ago, but the questions made me curious. According to Wikipedia: "Dopp kit is a term particularly in use in America for toiletry bags. The name derives from the early 20th century leather craftsman Charles Doppelt, whose company designed the case in 1926." So now we know.
I made one for my young grandson one time, and can tell you they're as easy to make as any bag.